A new synthetic method for preparing phosphorus imidate esters has been recently discovered which will enable us to prepare potentially important anti-tumor agents and esterase inhibitors. The generality of the synthetic method and the chemistry of the imidate esters will initially be investigated to further assess the possible biological use and functions of these compounds. Two general approaches will be employed in the actual design and synthesis of drugs: (1) chemically converting compounds of known importance of imidate derivates which would increase the selectivity of the medicinal; and (2) preparing imidates which are structurally and chemically analogous to known biologically important compounds. Finally, these imidate esters will be used to probe the nature of the active site in the esterase enzymes.